1. Field of the Invention
The present invention relates generally to delivery of Internet Protocol (IP) video content via a network from a source, such as a broadcaster, to users, such as subscribers to a broadcast service and, more specifically, to delivery of IP video content via a passive optical network (PON).
2. Description of the Related Art
Most digital telecommunications networks (i.e., networks that facilitate the communication of data, voice, video, etc., between parties or between a content distribution service and subscribers) typically comprise active components, such as repeaters, relays and other such devices that consume power, in the path between an exchange and a subscriber. In addition to requiring power, active components are subject to failure and performance degradation over time, and may require significant periodic maintenance. The passive optical network (PON) has been developed to overcome some of the deficiencies. The essence of a PON is that, but for the (active) electronic equipment at the exchange or central office end of the PON and subscriber end of the PON, the PON comprises nothing but optical fiber and passive components. A single fiber can run from the central office to a passive splitter located near a group of subscribers, such as a neighborhood or office complex, and individual fibers can run from the splitter to individual subscribers.
The International Telecommunications Union (ITU) and the Institute of Electrical and Electronics Engineers (IEEE) are two standards-making bodies currently developing PON standards. The ITU has adopted the recommendations of the Full Service Access Networks (FSAN) organization, including G983.x, a specification for Broadband PON (BPON), also referred to as “APON,” a reference to the Asynchronous Transfer Mode (ATM) data transmission protocol, and G984.x, a specification for Gigabit PON (GPON). These standards and recommendations are well-known to persons skilled in the art to which the invention relates.
In accordance with these standards, a PON comprises an optical line terminator (OLT) that is typically located at the central office and a number of optical network terminals (ONTs) (also known as optical network units (ONUs), each located at the subscriber's premises (e.g., home, office building, etc.), with optical fiber and splitters between the OLT and ONTs. In the downstream direction, i.e., data transmitted from the OLT (e.g., located at the exchange) to an ONT (e.g., located at a subscriber's premises), the data units (e.g., ATM data packets) are broadcast from the OLT to all of the ONTs on the PON, and an ONT can select the data to receive by matching the address embedded in the data units to a previously provisioned or learned address. In other words, an ONT only “listens” to data units having a matching address. Thus, the OLT can transmit data to a particular or selected ONT by addressing it to that ONT. In the upstream direction, i.e., data transmitted from an ONT to the OLT, the data units are time-domain multiplexed.
Interest has been expressed in using PONs to distribute compressed digital video (e.g., MPEG-encoded television (TV) content) to subscribers in the manner of a conventional, i.e., copper wire-based, digital cable television system, and in using Internet Protocol (IP) as the transmission protocol so that video delivery can be integrated efficiently with other digital services offered to the subscribers. The most straightforward scheme that has been considered involves broadcasting all available TV channels to all ONTs on the PON in a manner analogous to that in which a conventional cable TV system broadcasts the offered television channels to its subscribers, but it was recognized that bandwidth limitations would prohibit such a solution. To conserve bandwidth, other solutions that are more akin to multicast than broadcast have been proposed. Multicasting refers generally to distributing data to a defined group, and IP multicasting is a term that has been used to refer to distributing data to a group defined by a single IP address. The Internet Group Management Protocol (IGMP) is a well-known standard for IP multicasting.
The proposals for multicasting television channels using IP over PONs have involved creating connections between the OLT and ONTs in response to subscribers' requests to view television channels (e.g., by the subscriber entering a channel on a set-top box using a remote control). In many instances, “provisioning” prior to the time the system is actually used by subscribers is needed to provide an association between each IP TV channel and one of the connections that is to carry that TV channel.
An ONT can have several user ports, each of which can be connected to a compatible set-top box, computer or other device. For example, a subscriber can connect a set-top box and television located in one room of a home to one port and connect another set-top box and television located in another room to another port, so that several family members can watch television simultaneously.
When a subscriber requests to view a TV channel, the ONT at the subscriber's premises will attempt to service the request (locally) by providing the TV channel if at least one other user on the same ONT has been viewing the TV channel or, if no others have been viewing it, will request the TV channel from the OLT. The connections set up between the OLT and ONT to convey that the TV channel is being set up use the ONT Management and Control Interface (OMCI). OMCI is a service-level protocol that specifies the managed entities of a protocol-independent Management Information Base (MIB) that models the exchange of information between the OLT and an ONT. In addition, OMCI covers the ONT management and control channel protocol and the messages that are exchanged between the OLT and ONT for provisioning and setting up services at the ONT. The term “service-level” in this context refers to a high-level protocol, in contrast with the other, lower-level protocols, that the ONT protocol stack comprises. As well understood by persons skilled in the art to which the invention relates, a protocol stack is a group or suite of software elements, each itself defined by a protocol, that interact or communicate with each other in conformance with the networking protocol to which they collectively relate. The lowest-level protocol always relates to physical interaction with the hardware and typically has a very basic interface to the next-highest layer. OMCI, a service-level protocol, is near the top of the ONT protocol stack, while other layers of the ONT protocol stack, such as the Transmission Convergence (TC) layer, are near the bottom of the stack, near the hardware interface.
The OMCI message enables the OLT to set up a connection through which the data is delivered from the OLT to the subscriber's ONT. The ONT, in turn, delivers the data to a set-top box, which decodes the video signal and provides the decoded signal to a television set. The subscriber (user) operates the set-top box in the manner that is common in digital cable television systems, using a remote control to change TV channels, request video-on-demand, and so forth. When a subscriber requests a different TV channel or otherwise requests to drop the channel (e.g., turns off the set-top box), the virtual channel that was set up by the OLT to carry that TV channel to be dropped is deleted using OMCI.
The above-described mechanism for multicasting TV channels using IP over a PON suffers from deficiencies that include long channel setup latency. In other words, the time interval between the subscriber inputting the channel request and the subscriber's ONT beginning to receive the requested television channel is annoyingly long, perhaps on the order of several seconds. The long channel setup latency is due to the use of OMCI messaging between the OLT and ONT. Because OMCI is a service-level, i.e., high-level, protocol, it necessitates communication of several messages and acknowledgements between the OLT and ONT, thereby taking considerable time to set up a virtual channel. It may also involve operator provisioning to associate TV channels and virtual channels prior to operational deployment. It would therefore be desirable to provide a method and system for delivering IP video over a PON network that not only conserves bandwidth but that also does not suffer from excessive channel setup latency. The present invention addresses these problems and deficiencies and others in the manner described below.